On 1st January 2014 VMware published a new KB article, numbered 2068424, reporting an important issue for virtual machines backup.

If you meet these conditions:

– vSphere 5.5
– VMDK virtual disk at 2TB or bigger
– you use HotAdd mode to do backups

the backup ends immediately, it’s reported as completed successfully, but in reality it has failed. As you can imagine, this is even worst than a visible error because an administrator could be mislead by backup reports, and end up having a corrupted backup once he/she needs to do a restore.

At the moment there is NO solution, we can only wait for VMware to release a corrected version of VDDK (Virtual Disk Development Kit) 5.5.

If you are using Veeam Backup & Replication, you will have this error when your backup proxy is installed as a virtual machine. Since Veeam has other different backup methods, a workaround is to use Direct SAN (if it’s possible in your environment) or to deploy an additional virtual proxy, and configure it to explicitly use Network Mode, like this:

If you leave the default “Automatic selection”, backup is going to be done using “Virtual Appliance”, that is the mode that can lead to the bug.

Finally, you should create a new backup job, add to it all those VMs with at least one virtual disk at 2TB or above, and remove those VMs from other backup jobs using HotAdd/Virtual Appliance.

I will update this post when VMware will patch this bug.

EDIT: this issue has been solved with VDDK libraries 5.5.1. Please be sure to alway use the latest VDDK libraries to avoid known bugs.